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Alan L Alan L is offline
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Join Date: Apr 2006
Location: New Zealand
Posts: 3,247
a bit of diagnosis help

I have slight issue with #s 1&2 on my track machine. felt slightly down on grunt so did some diagnosis.
The CRs are down on 1&2 - 100 -105 compared to 120 on the rest.
Leakdown is 'OK' on all - 96-98% - but on a 040" or 1mm orifice.
Made a smaller orifice (030") and was down to around 85-90% on these two cylinders. A bit of this leak is clearly thru the exhaust valves. The rest is thru the crankcase.
My problem is if there is a serious issue, I need to tear it down and get in back in within a month. And my parts delivery via pelican is about 10 days. And that is about as quick as it gets with no local stuff on the shelf. So, I'm trying to second guess with these numbers what I might expect.
Would broken rings show up more? The valves are easy fixed hopefully. But anticipating the parts is harder. If it is not broken rings, would you get uneven ring wear on 2 cylinders? Can I just slot new rings in if that is the case - ie would it be worth ordering a set of rings before tear down.
So, any ideas on the likely diagnosis? I have a spare set of p&Cs - but bound to be the wrong group weight to deal with 2 cylinders. My guess is either broken rings, or worn rings - but I suspect the leakdown numbers are too good for broken rings?? - based on the standard 040 orifice. particularly when a decent amount of it is in the exhaust valves - these are the only two cylinders with E leak and any noticeable blowby - but it is noticeable via the crankcase.
One last Q - no head gaskets? What do I seal them up with?
Anyone had any experience with numbers like this?
83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 06-14-2011, 12:50 AM
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